FIG. 1 of the accompanying drawings is a schematic representation of a known aircraft ducted fan gas turbine engine 10 comprising, in axial flow series: an air intake 12, a propulsive fan 14 having a plurality of fan blades 16, an intermediate pressure compressor 18, a high-pressure compressor 20, a combustor 22, a high-pressure turbine 24, an intermediate pressure turbine 26, a low-pressure turbine 28 and a core exhaust nozzle 30. A nacelle 32 generally surrounds the engine 10 and defines the intake 12, a bypass duct 34 and a bypass exhaust nozzle 36. Electrical power for the aero engine and aircraft systems is generated by a wound field synchronous generator 38. The generator 38 is driven via a mechanical drive train 40 which includes an angle drive shaft 42, a step-aside gearbox 44 and a radial drive 46 which is coupled to the high pressure compressor 34 via a geared arrangement.
Air entering the intake 12 is accelerated by the fan 14 to produce a bypass flow and a core flow. The bypass flow travels down the bypass duct 34 and exits the bypass exhaust nozzle 36 to provide the majority of the propulsive thrust produced by the engine 10. However, a proportion of the bypass flow is taken off and fed internally to various downstream (hot) portions of the engine to provide a flow of relatively cool air at locations or to components as or where necessary. The core flow enters, in axial flow series, the intermediate pressure compressor 18, high pressure compressor 20 and the combustor 22, where fuel is added to the compressed air and the mixture burnt. The hot combustion gas products expand through and drive the sequential high 24, intermediate 26, and low-pressure 28 turbines before being exhausted through the nozzle 30 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines 24, 26, 28 respectively drive the high and intermediate pressure compressors 20, 18 and the fan 14 by interconnecting shafts 38, 40, 42.
In modern gas turbine engines the high pressure (HP) turbine gas temperatures are often now much hotter than the melting point of the materials commonly used for many of the HP turbine components, such as nozzle guide vanes (NGVs), turbine blades, as well as various other static and/or rotary parts (e.g. carriers, shrouds, platforms, etc) of the engine structure used to mount, support, carry or surround such components. It is therefore necessary to provide particularly efficient cooling of such components. In some engines efficient cooling also of components of the intermediate and low pressure turbines 26, 28 may also be especially desirable.
One of the challenges faced by engine designers is how to efficiently deliver a desired amount of cooling air, which is supplied from the HP compressor 20 having bypassed the combustor, to the required locations to the relevant components downstream of the combustor. This is often difficult, taking into account the complex engine architecture and the fact that many of the components in question that need most cooling are associated with especially high temperatures and mechanical stresses when in operation, which makes the accommodation of differential expansion of such components and/or their carriers, shrouds, platforms, etc also a particularly challenging task.
A feature of a typical modern engine in respect of which efficient delivery of cooling air to hot components is especially important is the carrier portion of the HP turbine section which supports the NGVs and the segments of which at least partially surround the turbine blades. This particular section of a typical engine is shown in FIGS. 2 and 3(a), (b) and (c) of the accompanying drawings. Here a series of segments 50 are united together circumferentially around the engine to form a complete, generally annular, segmented blade track liner section or ring for supporting the NGVs and partially enshrouding the turbine blades (not shown). The segments 50 are disposed radially inwardly of the engine outer casing (components of which are shown generally as 46), and also shown here are flap seal 47 for pinning to an NGV, recess 48 for accommodating a respective NGV anti-rotation lug, an anti-rotation lug 56 for anchoring the segment 50 (or rather anchoring the carrier 60 which carries the segment 50) in place relative to the casing 46, and flap plate rail or flange 49 for use in the sealing arrangement to form a seal between the hot inboard region and the cooler outboard region within the HP turbine architecture.
Each segment 50 is carried by a generally flat carrier 60 in the form of a wall defining radially inwardly thereof (i.e. therebeneath, in the orientation shown in FIGS. 2 and 3) part of a radially inward main cooling chamber 70 for receiving cooling air from an outboard feed source via a series of elongate conduits 90 formed in a forward end wall section 52F of the carrier 60 (or segment 50). The main cooling chamber 70 is that section of the arrangement which at least partially enshrouds the turbine blades. The carrier 60 also defines radially outwardly thereof (i.e. thereabove, in the orientation shown in FIGS. 2 and 3) a radially outward secondary chamber 80 which ideally needs to be thermally divorced from (or rather “stagnant” relative to) the main cooling chamber 70 in order to optimise the latter's cooling efficiency. Because of the high axial thrust loads typically exerted by the NGVs on the carrier 60 during use, the carrier 60 is arranged so as to extend between the front 52F and rear 52R end sections or walls of the carrier 60 (or segment 50) at an inclined angle relative to the engine axis.
With this known arrangement, however, the efficient delivery of cooling air to the main radially inward cooling chamber 70 presents practical difficulties. The main issue is how to get sufficient flow rates of cooling air from the outboard feed source into the radially inward cooling chamber 70 efficiently, yet past the critical sealing arrangement involving the flap plate rail or flange 49 which separates and seals the hot NGV-containing region from the cooler outboard region via which the cooling air is fed. Because of the loading necessity for the inclined carrier wall 60 to have its front end at a radially inward location relative to the radially outward cooling air feed source, where the front end section 52F of the carrier 60 (or segment 50) is at its fattest, the fact that the flap plate rail sealing flange arrangement 49 in effect blocks easy access from the outboard feed source to the main cooling chamber 70 leads to a difficulty in providing a localised geometry or architecture that meets these conflicting requirements in an efficient manner.
Current designs of carriers and segments address this issue by using a series of elongate conduits 90 cast or drilled through the front end section or wall 52F of each carrier 60 (or segment 50). However this involves either drilling through large volumes of material, which is time-consuming, costly and wasteful, or alternatively using complex casting techniques, which is also time-consuming and costly. It is not possible simply to move the conduits 90 radially outwardly so as not to have to pass through the large volumes of carrier end section or wall 52F, because this would still involve drilling through at least two wall sections, which defeats the object.
Thus there is a need in the art for a more efficient way of meeting the above conflicting criteria and providing a more efficient arrangement for enabling sufficient flow rates of cooling air from an outboard feed source into the radially inward cooling chamber 70 without having to pass the NGV sealing arrangement. This is therefore a primary object of the present invention.